Here we present a status report of the first spherical antenna project equipped with a set of parametric transducers for gravitational detection. The Mario Schenberg, as it is called, started its commissioning phase at the Physics Institute of the University of São Paulo, in September 2006, under the full support of FAPESP. We have been testing the three preliminary parametric transducer systems in order to prepare the detector for the next cryogenic run, when it will be calibrated. We are also developing sapphire oscillators that will replace the current ones thereby providing better performance. We also plan to install eight transducers in the near future, six of which are of the two-mode type and arranged according to the truncated icosahedron configuration. The other two, which will be placed close to the sphere equator, will be mechanically non-resonant. In doing so, we want to verify that if the Schenberg antenna can become a wideband gravitational wave detector through the use of an ultra-high sensitivity non-resonant transducer constructed using the recent achievements of nanotechnology.
Abstract. The first phase of the Brazilian Graviton Project is the construction and operation of the gravitational wave detector Mario Schenberg at the Physics Institute of the University of São Paulo. This gravitational wave spherical antenna is planned to feature a sensitivity better than h = 10 -21 Hz -1/2 at the 3.0-3.4 kHz bandwidth, and to work not only as a detector, but also as a testbed for the development of new technologies. Here we present the status of this detector.
Abstract. This work reports improvements made in the modelling of mechanical impedance matchers with mushroom shape using the finite elements method when shell elements type were used instead of tetrahedron elements type. Also, it is presented here an original methodology which makes use of the symmetry of the system and its influence on the mechanical vibrational modes to validate the modelling that was the base for the simulations performed.
An experiment to measure the speed of gravitational signals in short distances has been developed with the goal to study its behaviour as traveling through a medium different from air. The experiment is composed of three sapphire devices suspended in vacuum and cooled down to 4.2 Kelvin. The amplitudes of the central device (detector) is monitored by an ultralow phase noise microwave signal using resonance in the whispering gallery modes. The other two sapphire devices are excited by piezoelectric crystals, which make the two devices vibrate at the same frequency and phase. Between the two vibrating devices and the detector, a different medium will be placed, and then the speed is measured and compared with the case where the medium is pure air. The modelling of the experiment is made assuming the detector as a spring-mass system. The results show that the detection is achievable.
In order to investigate the behavior of gravitational signals while travelling through a medium an experiment was designed, aimed at measuring the speed of these signals over short distances. The experiment contains 2 sapphire vibrating devices that emit a signal and one sapphire device that behave as a detector, which are suspended in vacuum and cooled down to 4.2 K. The amplitude of the detecting device is measured by an ultralow, phase-noise microwave signal that uses resonance in the whispering gallery modes. Since sapphire has a quite high mechanical Q, the detection band is expected to be small, thus reducing the detection sensitivity. A new shape for the detecting device is presented in this work, yielding a detection band of several hundred Hertz. With the aid of a Finite Element Program the normal mode frequencies of the detector are determined assuming the detector as a spring-mass system. The results show that the detection is achievable then the best operational frequency is determined.
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An experiment to measure the speed of gravity is being planned. For this purpose, a numerical method was developed for the optimization of a composite quadrupole mass at high-speed rotation. The optimization calculations aim to obtain a quadrupole mass which must generate a periodic gravitational signal of 3200 Hz with maximum amplitude, taking into account its geometric features and the mechanical properties of the component materials. Considering the gravitational wave detector Mario Schenberg as the signal receiving device, an estimate was obtained in which the largest emitterdetector distance for detecting the gravitational signal is between the orders of magnitude 10 1 and 10 2 m. A simplified modeling of the emitter-detector system indicates that the gravitational signal amplitude h decreases approximately proportional to r À5 , where r is the emitter-detector distance. The results obtained in this work serve as reference for more detailed numerical simulations in the future.
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